1. Field of the Invention
The present invention relates generally to a device which burns gas, and more particularly to a protective device for a gas appliance operating in an environment with insufficient oxygen.
2. Description of the Related Art
Gas appliance is a device which burns gas to heat something, such as water heater, gas stove, or fireplace. The common accident caused by the gas appliance is carbon monoxide poisoning. The carbon monoxide is produced from incomplete burning, and there will be an incomplete burning if the gas appliance is operating in a poor ventilation environment. Carbon monoxide is colorless and odorless to kill people in silent.
In complete burning, the gas appliance will generate carbon dioxide and water, and carbon monoxide will be generated from incomplete burning. The accident usually happens in wintertime, people close the windows, and that will stop the ventilation in the room. If the gas appliance is operating in that room, carbon monoxide will quickly accumulated in the room and cause accident.
Oxygen is an important element for life. Earth's atmosphere contains roughly 78.08% nitrogen, 20.95% oxygen, 0.93% argon, 0.03% carbon dioxide, and other rare gases. Typically, oxygen concentration should be 20.5% or more in a normal room to keep human's life, and in a government's rule, there should be at least 18% oxygen in a room.
In order to avoid the incomplete burning in the gas appliance when it is operating in a room of poor ventilation, a security device is provided to be incorporated in the gas appliance. A conventional security device includes a thermocouple 50 and a gas valve 60. The thermocouple 50 is around a burner 40 of the gas appliance to generate a thermoelectric potential because of a heat of the burner 40. The gas valve 60 has a coil 62, a magnet 64, a spring 66, and a gate 68. The coil 62 is electrically connected to the thermocouple 50 to receive the thermoelectric potential and generate a magnetic field to attract the magnet 64 so as to compress the spring 64, and then the gate 68 will be opened to supply the burner 40 with gas. It is easy to understand that the heat of the burner 40 is inversely proportional to the gate 68 to be opened. The gate 68 will be opened wider while the heat of the burner 40 is higher, and the gate 68 will be closed while the heat is lower than a predetermined level. So that, if incomplete burning occurs, the heat of the burner 40 drops to make the gate 68 be closed a little to reduce the gas for the burner 40, and if the incomplete burning becomes more and more serious, the gate 68 will be totally closed to cut off the gas.
It is obvious that the conventional security device is working by magnetic force and spring force. Fatigue and jam of the elements will make the security device malfunction or failure.